1. Field of the Invention
The present invention relates to drive devices for driving switching elements of a voltage controlled type. For example, such switching elements are power switching elements used in an inverter and a convertor which are placed between a motor generator and a high-voltage power source mounted on vehicles such as hybrid vehicles.
2. Description of the Related Art
There is a conventional drive device for driving a switching element such as a power switching element. The power switching element is used in an inverter or a converter placed between a motor generator and a high-voltage power source mounted on a hybrid vehicle.
For example, a conventional document, Japanese patent laid open publication No. JP 2009-71956 discloses such a drive device equipped with a pair of power sources, a high voltage power source and a low voltage power source. The power sources supply a different voltage to the gate terminal of a switching element such as a gate bipolar transistor (IGBT) in order to turn on the IGBT. An inverter and a converter are equipped with a plurality of IGBTs. In order to turn on the IGBT, one of the power sources supplies a low voltage to the gate terminal of the IGBT.
Next, the other power source supplies a high voltage to the gate terminal of the IGBT in order to increase the voltage potential of the gate terminal of the IGBT. This makes it possible to efficiently avoid an excess current from generating and flowing in the IGBT. Further, this makes it possible to decrease a conductive loss because of rapidly increasing the voltage of the gate terminal of the IGBT when there is no possibility to flow such an excess current in the IGBT.
However, the conventional drive device having the structure described above has a drawback where a current flows from a high voltage side to a low voltage side when the high voltage power source supplies power to the gate terminal of the IGBT. In order to solve this problem, the conventional drive device is equipped with a diode to inhibit such a current from flowing. However, the above conventional solution using the diode would cause a problem for the voltage of the gate terminal of the IGBT to fluctuate.
Because the above conventional drive device is equipped with the pair of the power sources such as a high voltage power source and a low voltage power source, the entire circuit size of the drive device is increased, and the manufacturing cost thereof is also increased.